Existing single cantilever tubular spar wing designs?

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dog

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talking about tapered thickness spars - the Gossamer Condor or its offspring used an aluminum spar that was etched towards the tip. Cannot remember the etchant: caustic soda ??
When building the gosemer condor they needed
tubular carbon spars,that they built on aluminum
tubing and then dissolved the aluminum, as it was the only way to free the carbon.
Didnt know about chemical tapering, could be done simply by dipping, like a candle in reverse.
 
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I have read of some of the other above and beyond treatments from the bad old days, but not this one. I'd love to read about it if you have an idea of where to look for it...
I wish I had the actual report as well. But I got it first hand from the principal research Engineer doing the work. Since I cannot produce the proof I probably should have said something like "The US Air Force Labs purportedly..."
 

SMORGAN

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I have a book called Gossamer Odyssey by Morton Grosser, the Condors tube structure was etched internally with swimming pool chlorine I think. By filling the tubes when vertical and the chemicals poured in at the top then the lower part of the tube was etched more than the top due to the length of time in contact with the chemical. Probably needed a bit of experimentation. For the Albatross the carbon was wrapped at various angles to give the strength needed and the aluminium was etched out completely.
See the attached images.


DSCN9168.JPGDSCN9169.JPG
 

TFF

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Back in the day, Model Aviation had an article on the electric Solar one as it was powered by an RC motor. There was one picture of wrapping the spar.
 

rv7charlie

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Thanks for the references to the various iterations of the human powered stuff; was too easy for me to forget there were multiple versions. The distinctive one for me was the pure carbon version, with the aluminum completely etched away.
 

Bigshu

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On round tube spars in general: What VB said about structural efficiency; to be strong enough at the root, they're waaay overbuilt along the length to the tip. There's also the compromise of picking up a bit torsional rigidity (inefficiently), but wasting a lot of structure weight in the 'web' area of the spar. Offsetting that is the incredible ease of assembly when the spar is 'pre-assembled', and you can just slide the ribs onto the spar and jig them into alignment.
I wonder how CF tubes, which can have the thickness varied from end to end as they're wound, would work in this application? Seems like not wasting structural weight in the tips, but keeping the tube diameter constant for assembly would be a win-win.
 

rv7charlie

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Interesting thread. How did Bede add dihedral to the centre section tube spar?

James.
I don't know about the BD-4C, but the on the original, he didn't. With no loading, they were perfectly straight, tip to tip. The planes had slight anhedral when sitting on the ground due to the 'dead' weight of the wings & fuel, and very slight dihedral in flight due to lifting bending loads on the wings (think sailplane; not so much). I know some of the original wings had sump drains added to the outboard end of the wing tanks, so any water could be cleared.
 

TFF

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BD-5 is bent. I guess the Grummans are too. I’m sure the strength change is calculated.
 
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